It has been a common practice to authenticate a written document by the signature of the author or by some similar means. Thus, for example, a typical letter includes both the text and the signature of the writer. The latter serves not only to identify the author but also indicates that he acknowledges authorship and in general authenticates the letter to the recipient thereof. Other documents such as, for example, purchase orders, also typically provide for signatures to indicate authenticity. Historically, letters and other documents have been physically transported to points remote from the sender by means of the mail service or private carrier.
As the cost of transportation rises and thus the cost of the mail service rises electronic means are being considered to "transport" the mail. In such a system the contents of letters and other documents are converted to electronic form or, if originating in electronic form (such as computer-generated bills), are maintained as such and suitably transmitted to the selected remote point. Some means of authentication or approval of such electronically-transmitted documents must be provided. The conventional facsimile processor for reading both the text of a document and an author's signature or mark and transmitting the same are too slow and expensive for transmission of large amounts of mail. Digital means of scanning and transmitting the printed text of a letter or other document or transmitting computer generated information while fast and relatively inexpensive, is not readily adapted to transmit written authentication.